The present invention relates to a motor and, more particularly, to a motor which has dynamic pressure type bearings.
Heretofore, a conventional motor having dynamic pressure type bearings includes in general a housing having a horizontal bottom, and a stationary shaft vertically placed upright on the bottom. A cylindrical rotational shaft, on which a rotor is mounted, is rotatably engaged on the outer periphery of the stationary shaft. This motor also has a radial load dynamic pressure type bearing and a thrust load dynamic pressure type bearing. The radial load dynamic pressure type bearing has an air groove formed on the outer peripheral surface of the stationary shaft. When the rotational shaft is rotated, the air groove serves to generate a dynamic pneumatic flow between the outer peripheral surface of the stationary shaft and the inner peripheral surface of the rotational shaft, thereby bearing the radial load of the rotational shaft. The thrust load dynamic pressure type bearing has an air groove formed on the bottom. When the rotational shaft is rotated, the air groove serves to generate a dynamic pneumatic flow between the bottom and the lower end surface of the rotational shaft, thereby bearing the thrust load of the rotational shaft.
In order to generate the above-described dynamic pneumatic flow, the respective members should be machined to a high dimensional accuracy. In other words, in the case of the above-mentioned conventional motor, it is constructed to generate dynamic pneumatic flows between the outer peripheral surface of the stationary shaft and the inner peripheral surface of the rotational shaft, and between the lower end surface of the rotational shaft and the bottom of the housing. Hence, these surfaces of the members should be machined to a high dimensional accuracy. Further, when the dynamic pneumatic flow is generated between the lower end surface of the rotational shaft and the bottom of the housing to bear the thrust load of the rotational shaft, the bottom is required to be as perpendicular as possible with respect to the stationary shaft. Accordingly, the stationary shaft and the bottom should be machined to a further high accuracy. Thus, the conventional motor has more members which must be formed with a high degree of accuracy. The motor requires several complicated steps of manufacture, and so its high cost is also a drawback.